For transmission of digital data, the signals are modulated on a carrier by means of a modulator. A known principle for a direct modulator used in transmission has carrier and signal inputs and a signal output interconnected as follows. The carrier input and the signal output are connected by two paths, one of which contains a phase delay element. Furthermore, each of the two paths contains a non-linear semiconductor component arranged in such a way that the non-linear semiconductor components, by virtue of their polarity and the arrangement of the phase delay element, which provides a phase delay of 180.degree., are switched in unison with reference to the carrier, such that the carrier is extinguished at the signal output. If a signal in the form of a modulation voltage is introduced into the delay path, the two non-linear semiconductor elements will be switched in push-pull fashion with reference to the modulation voltage, which causes the modulation of the carrier at the signal output. Such a modulator can also be used as a mixing stage. A particular structure of a modulator working on the principle described above, and its use as a mixer, is described in the German Patent Document 29 44 642, which generally corresponds to U.S. Pat. No. 4,249,263 hereby incorporated by reference. The phase delay element of the described modulator consists of a piece of conductive material having the length .lambda./2 of the midfrequency of the carrier.
Because of the rigidly defined length of the phase delay element, the known amplitude modulator teaches only a predetermined length, namely .lambda./2 of the carrier.